Process for the manufacture of 1,2-dichloroethane

ABSTRACT

Process for the manufacture of 1,2-dichloroethane (DCE) starting from a stream of ethane which is subjected to a catalytic oxydehydrogenation (ODH) producing a gas mixture containing ethylene then dried and subjected to an absorption to be separated into a fraction enriched with the compounds that are lighter than ethylene containing some of the ethylene conveyed to a chlorination reactor R 1  in which most of the ethylene is converted into DCE, and into a fraction F 1  which is subjected to a desorption D 1  to be separated into an ethylene fraction depleted of the compounds that are lighter than ethylene conveyed to a chlorination reactor R 2 , the stream of products derived from this reactor being added to the dry gas mixture, and into a fraction F 2 . Fraction F 2  is then subjected to a desorption D 2  to be separated into a fraction enriched with ethylene conveyed to an oxychlorination reactor in which most of the ethylene is converted into DCE, and into a fraction F 3  which is recycled to the absorption.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. national stage entry under 35 U.S.C.§371 of International Application No. PCT/EP2007/056227, filed Jun. 22,2007, which claims benefit of French patent application No. 06.05718filed on Jun. 26, 2006, all of these applications being hereinincorporated by reference in their entirety for all purposes.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a process for the manufacture of1,2-dichloroethane (DCE), a process for the manufacture of vinylchloride (VC) and a process for the manufacture of polyvinyl chloride(PVC).

BACKGROUND

DCE is usually prepared by oxychlorination of ethylene using hydrogenchloride (HCl) and a source of oxygen or by direct chlorination ofethylene using chlorine. The dehydrochlorination of DCE by pyrolysisthus results in the production of VC with release of HCl. Theoxychlorination and chlorination are generally carried out in paralleland the HCl produced in the pyrolysis is used in the oxychlorination.

To date, ethylene which is more than 99.8% pure is normally used for themanufacture of DCE. This very high purity ethylene is obtained via thethermal cracking of various petroleum products, followed by numerouscomplex and expensive separation operations in order to isolate theethylene from the other products of the cracking and to obtain a productof very high purity.

Given the high cost linked to the production of ethylene of such highpurity, and also the advantage that there could be in envisaging aprocess for the manufacture of VC by DCE in favourable regions that lackaccessible ethylene capacities, various processes for the manufacture ofDCE using ethylene having a purity of less than 99.8% have beenenvisaged. These processes have the advantage of reducing the costs bysimplifying the course of separating the products resulting fromcracking of petroleum products and by thus abandoning complexseparations which are of no benefit for the manufacture of DCE.

Thus, various processes for the manufacture of DCE starting fromethylene having a purity of less than 99.8% produced by simplifiedcracking of ethane have been envisaged.

For example, Patent Application WO 00/26164 describes a process for themanufacture of DCE by chlorination of ethylene obtained by simplifiedcracking of ethane, the chlorination taking place in the presence ofimpurities obtained during the cracking of ethane without any otherpurification.

Patent Application WO 03/48088 itself describes a process for themanufacture of DCE by dehydrogenation of ethane giving rise to theformation of a fraction comprising ethane, ethylene and impuritiesincluding hydrogen, which fraction is then subjected to a chlorinationand/or oxychlorination.

These processes have the disadvantage that the ethylene obtained cannotbe used for a combined ethylene chlorination/oxychlorination processgiven that the ethylene contains impurities whose presence during theoxychlorination reaction could cause operating problems, namelypoisoning of the catalyst by the heavy products and an uneconomicconversion of the hydrogen present. This hydrogen conversion wouldconsume high-purity oxygen which would thus be sacrificed for anundesired reaction and would release a high heat of reaction during theconversion of hydrogen to water. This conversion would then limit thecapability of the oxychlorination reactor, generally linked to the heatexchange capability. An unusually high investment must therefore beexpended in order to guarantee the heat exchange area, and thereby thereactor volume, caused by the presence of hydrogen in the mixture.

The option taken of burning the hydrogen in a separate reactor,described in Application WO 03/48088, does not resolve the difficultybecause it requires a large amount of oxygen, a stoichiometric amountrelative to hydrogen, and also a large surface area for exchange toeliminate this heat of combustion. Consequently it has a significantethylene consumption and it may have problems linked to safety. Finally,the removal of the water formed leads to an increase in the productioncosts.

Processes in which VC is obtained by oxychlorination of ethane and notof ethylene are also known. Such processes have not found an industrialapplication up till now given that as they are conducted at hightemperatures, they result in a mediocre selectivity with loss of thereactants used and costs for separating and destroying the by-productsand they are also characterized by problems of behaviour of thematerials in a corrosive oxychlorination medium. Finally, problemslinked to the behaviour of the catalysts used owing to the gradualvaporization of their constituents and also linked to the deposition ofthese constituents on the cold surface of the exchanger bundle areusually encountered.

SUMMARY OF THE INVENTION

One object of the present invention itself is to provide a process usingethylene having a purity of less than 99.8% which has the advantage ofreducing the costs linked to the production of ethylene of higher purityand which has the advantage of avoiding the abovementioned problems.

To this effect, the invention relates to a process for the manufactureof 1,2-dichloroethane starting from a stream of ethane according towhich:

-   a) the stream of ethane is subjected to a catalytic    oxydehydrogenation producing a gas mixture containing ethylene,    unconverted ethane, water and secondary constituents;-   b) said gas mixture is optionally washed and dried thus producing a    dry gas mixture;-   c) after an optional additional purification step, said dry gas    mixture comprising the stream of products derived from the    chlorination reactor R2 separated in step e) is subjected to an    absorption A which consists of separating said gas mixture into a    fraction enriched with the compounds that are lighter than ethylene    containing some of the ethylene (fraction A) and into a fraction F1;-   d) fraction A is conveyed to a chlorination reactor R1 in which most    of the ethylene present in fraction A is converted into    1,2-dichloroethane and the 1,2-dichloroethane obtained is separated    from the stream of products derived from the chlorination reactor    R1;-   e) fraction F1 is subjected to a desorption D1 which consists of    separating fraction F1 into an ethylene fraction depleted of the    compounds that are lighter than ethylene (fraction C) which is    conveyed to a chlorination reactor R2, the stream of products    derived from this reactor being added to the dry gas mixture    subjected to step c) after having optionally extracted the    1,2-dichloroethane formed, and into a fraction F2;-   f) fraction F2 is subjected to a desorption D2 which consists of    separating fraction F2 into a fraction enriched with ethylene    (fraction B) and into a fraction F3, optionally containing the    1,2-dichloroethane formed in the chlorination reactor R2 then    extracted, if it has not previously been extracted, which is    recycled to the absorption A, optionally after an additional    treatment intended to reduce the concentration, in fraction F3, of    the compounds that are heavier than ethane;-   g) fraction B is conveyed to an oxychlorination reactor in which    most of the ethylene present in fraction B is converted into    1,2-dichloroethane, the 1,2-dichloroethane obtained is separated    from the stream of products derived from the oxychlorination reactor    and is optionally added to the 1,2-dichloroethane formed in the    chlorination reactor R1 and optionally to that formed in the    chlorination reactor R2; and-   h) the stream of products derived from the oxychlorination reactor,    from which the 1,2-dichloroethane has been extracted, optionally    containing an additional stream of ethane previously introduced in    one of steps b) to g), is optionally recycled to step a) after    having been optionally purged of gases and/or after an optional    additional treatment in order to eliminate the chlorinated products    contained therein.

BRIEF DESCRIPTION OF THE DRAWING

For a detailed description of the invention, reference will now be madeto the accompanying drawing in which:

FIG. 1 schematically represents an embodiment of the process for themanufacture of DCE according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

According to step a) of the process according to the invention, thestream of ethane is subjected to a catalytic oxydehydrogenationproducing a gas mixture containing ethylene, unconverted ethane, waterand secondary constituents.

The stream of ethane subjected to the catalytic oxydehydrogenation mayor may not be chemically pure. The stream of ethane used may contain upto 70 vol % of other gases such as methane, hydrogen, ethylene, oxygen,nitrogen and carbon oxides.

The stream of ethane used advantageously contains at least 80 vol %,preferably at least 90 vol %, particularly preferably at least 95 vol %and most particularly preferably at least 98 vol % of ethane. Ifnecessary, the ethane may be separated from the secondary compoundshaving a higher boiling point in any known device, for example byabsorption, extraction, diffusion or distillation.

The stream of ethane subjected to the catalytic oxydehydrogenation maybe a source of ethane such as is available on the market but also thestream of products derived from the oxychlorination reactor, from whichthe 1,2-dichloroethane has been extracted, optionally containing anadditional stream of ethane added to one of steps b) to g) and recycledin step h), or a mixture of the two.

The term “catalytic oxydehydrogenation (ODH)”, also known as catalyticoxidative dehydrogenation, is understood to mean a partial oxidation ofethane by oxygen in the presence of a catalyst.

ODH may take place either at a temperature above 650° C. up to 800° C.,below the range of thermal cracking temperatures, or at a temperatureless than or equal to 650° C.

The pressure at which step a) is carried out is advantageously at least1, preferably at least 1.5 and particularly preferably at least 2 barabsolute. It is advantageously at most 16, preferably at most 11 andparticularly preferably at most 6 bar absolute.

The oxygen introduced may be oxygen or a gas containing oxygen withother inert gases, such as for example air. Preferably, oxygen is used.The oxygen may or may not be chemically pure. Thus, it is possible touse a very pure source of oxygen containing at least 99 vol % of oxygenbut also a source of oxygen containing less than 99 vol % of oxygen. Inthe latter case, the oxygen used advantageously contains more than 90vol % and preferably more than 95 vol % of oxygen. A source of oxygencontaining from 95 to 99 vol % of oxygen is particularly preferred.

The amount of oxygen introduced, based on the amount of ethane, isadvantageously from 0.001 to 1 mol/mol, preferably from 0.005 to 0.5mol/mol and particularly preferably from 0.05 to 0.3 mol/mol.

ODH may be carried out in any known device. Advantageously, ODH iscarried out in one reactor or a series of reactors of fixed bed typehaving one or more beds, between which a thermal conditioning step maybe carried out, or in one reactor or a series of reactors of fluid bedtype, preferably adiabatic or with temperature control using anauxiliary fluid inside the reactor (multitubular reactor or heatexchanger immersed in the catalytic bed) or outside the reactor. Thereactants may be previously mixed before introduction into the reactionzone. One or more reactants may also be added differently, for examplebetween the beds of a multi-bed reactor. The reactor may be equippedwith preheating means and with any means necessary to control thereaction temperature. A cross exchanger advantageously enables the heatof the products formed to be recovered to reheat the incoming products.

Various catalytic systems may be used to carry out ODH according to theinvention.

Thus, mention may be made of catalysts based on alkaline-earth oxides,such as for example Li/MgO catalysts generally operating at temperaturesabove 600° C. Mention may also be made of catalysts based on nickel(Ni). Catalysts containing molybdenum (Mo) and/or vanadium (V) have aparticular advantage. These catalysts are generally based on oxides ofthese elements. They advantageously contain, in addition, other elementssuch as, for example Cr, Mn, Nb, Ta, Te, Ti, P, Sb, Bi, Zr, Ni, Ce, Al,Ca or W.

Catalysts based on vanadium (V) are most particularly advantageous.

Mixed oxides containing V and at least one other element chosen from Mo,W, Nb, Ta, Te, Ti, P, Sb, Bi, Zr, Ni, Ce, Al and Ca are preferred.

Mixed oxides containing both Mo and V, W and V or Mo, W and V areparticularly preferred.

Among those containing Mo and V, mention may be made of Mo—V—O,Mo—V—Zr—O, Mo—V—Ta—Sb—Zr—O, Mo—V—Ta—Sb—O, Mo—V—Nb—Te—O, Mo—V—Nb—Bi—Ni—O,Mo—V—Nb—Bi—O, Mo—V—Nb—Ni—O, Mo—V—Nb—Sb—Ca—O, Mo—V—Ta—Al—O, Mo—V—Ta—O,Mo—V—Al—O, Mo—V—Sb—O, Mo—V—Nb—O and Mo—V—Nb—Sb.

Among those containing W and V, mention may be made of W—V—O, W—V—Nb—O,and W—V—Ta—O.

Among those containing Mo, W and V, mention may be made ofMo—W—V—Ta—Te—Ti—P—Ni—Ce—O, Mo—W—V—Ta—Te—Ti—P—O, Mo—W—V—Te—Ti—P—Ce—O,Mo—W—V—Te—Ti—P—Ni—O, Mo—W—V—Te—Ti—P—O, Mo—W—V—Te—Ti—O, Mo—W—V—Te—P—O,Mo—W—V—Te—O, Mo—W—V—Ta—Te—Ti—P—Ni—Ce—O, Mo—W—V—Ta—Te—Ti—P—O,Mo—W—V—Te—Ti—P—Ce—O, Mo—W—V—Te—Ti—P—Ni—O, Mo—W—V—Te—Ti—P—O,Mo—W—V—Te—Ti—O, Mo—W—V—Te—P—O, Mo—W—V—Te—O, Mo—W—V—Nb—O, Mo—W—V—Sb—O,Mo—W—V—Ti—Sb—Bi—O, Mo—W—V—Ti—Sb—O, Mo—W—V—Sb—Bi—O, Mo—W—V—Zr—O,Mo—W—V—Nb—Ta—O, Mo—W—V—Nb—O and Mo—W—V—O.

Ta—Ni—O, Nb—Ni—O and Nb—Ta—Ni—O catalysts could also be used.

The catalysts used for ODH may or may not be supported. In the casewhere they are supported, the support which may possibly be usedincludes silica, alumina, titanium oxide, silicon carbide, zirconia andmixtures thereof such as mixed oxides.

The catalysts used for ODH are advantageously resistant to DCE.

The catalyst used may be placed on a bed or in tubes or outside of thosetubes so that a temperature control may be obtained by a fluidsurrounding these tubes or running through them.

ODH of the stream of ethane gives a gas mixture containing ethylene,unconverted ethane, water and secondary constituents. The secondaryconstituents may be carbon monoxide, carbon dioxide, hydrogen, variousoxygen-containing compounds such as, for example, acetic acid oraldehydes, nitrogen, methane, oxygen, optionally acetylene andoptionally organic compounds comprising at least 3 carbon atoms.

According to a first variant of the process according to the invention,ODH takes place at a temperature above 650° C. up to 800° C.

According to a second variant of the process according to the invention,ODH takes place at a temperature less than or equal to 650° C.

Advantageously, ODH then takes place at a temperature less than or equalto 600° C., preferably less than or equal to 550° C., particularlypreferably less than or equal to 500° C., more particularly preferablyless than or equal to 450° C. and most particularly preferably less thanor equal to 400° C. A temperature between 200 and 400° C. isparticularly advantageous.

In this case, the process according to the invention has the advantageof generating very small amounts of hydrogen responsible for manydrawbacks.

According to this second variant, advantageously ODH makes it impossibleto generate heavy compounds having a number of carbon atoms greater thanor equal to 3, such as for example propylene and olefins whose molecularweight is higher than that of propylene, in troublesome amounts.

The second variant of the process according to the invention ispreferred to the first.

According to step b) of the process according to the invention, said gasmixture obtained in step a) is optionally washed and it is dried thusproducing a dry gas mixture.

The gas mixture obtained in step a) may or may not be washed.Preferably, it is washed. Washing of the gas mixture obtained in step a)may be carried out by any known means. Preferably, it is carried outusing an aqueous, preferably alkaline, washing liquid, or using anon-aqueous liquid. Among the aqueous washing liquids, mention may bemade of sodium hydroxide, sodium carbonate, sodium hydrogen carbonateand sodium hydroxide. Among the non-aqueous liquids, mention may be madeof methylpyrrolidone, heavy oils and methanol. By this operation, solidssuch as coal, sulfur compounds, carbon dioxide, saturated or unsaturatedhydrocarbons that are heavier than ethylene, acetylene, acid speciessuch as acetic acid or hydrogen chloride, and aldehydes areadvantageously removed.

Drying of the gas mixture may then be carried out by any known means.Preferably, drying is carried out by cooling at the end of a compressionof the gases and/or by adsorption on a solid desiccant such as amolecular sieve, alumina or lime.

The washing step, when it takes place, and the drying step may takeplace in any order. Thus, it is possible to wash and then dry the gasmixture or to dry it and then wash it. Preferably, said gas mixtureobtained in step a) is washed then it is dried, thus producing a dry gasmixture.

After step b), the amount of water in the dry gas mixture isadvantageously less than or equal to 500 ppm, preferably less than orequal to 10 ppm and particularly preferably less than or equal to 1 ppmby volume.

An additional purification step, preferably a chemical purificationstep, of the stream subjected to chlorination in the chlorinationreactor R1 may be envisaged before it enters into the chlorinationreactor in order to remove therefrom any compound that is not desired inthe chlorination. This may be the case for acetylene, for example,formed during step a) but also for oxygen which is undesired when inexcess.

The acetylene may advantageously be removed via a hydrogenation,preferably by means of the hydrogen present in the mixture.

This step may take place prior to another step of the process accordingto the invention if that proves necessary, such as for example beforestep c), before the chlorination step in the chlorination reactor R2 orbefore the oxychlorination step. Preferably, when it takes place, ittakes place before step c).

After step b) defined above and the abovementioned optional additionalpurification step, said dry gas mixture comprising the stream ofproducts derived from the chlorination reactor R2 separated in step e)(known hereinafter as gas mixture) is subjected to step c) of absorptionA which consists of separating said gas mixture into a fraction enrichedwith the compounds that are lighter than ethylene containing some of theethylene (fraction A) and into a fraction F1.

Thus, the gas mixture is subjected to an absorption step A in which saidstream is preferably brought into contact with a washing agentcontaining DCE.

The expression “washing agent containing DCE” or more simply “washingagent” is understood to mean a composition in which the DCE is presentin the liquid state.

The washing agent that can be used for the absorption step A thereforeadvantageously contains DCE in the liquid state. The presence, in saidwashing agent, of other compounds is not at all excluded from the scopeof the invention. However, it is preferred that the washing agentcontain at least 50 vol % of DCE, more particularly at least 80 vol %and most particularly preferably at least 95 vol %.

The washing agent used for the absorption step A may be composed offresh washing agent of any origin, for example crude DCE exiting thechlorination unit, crude DCE exiting the oxychlorination unit or amixture of the two which has not been purified. It may also be composedof said DCE that has been previously purified, of the stream of productsderived from the chlorination reactor R2 when the DCE is not extractedtherefrom in so far as it is first liquefied, or of all or part offraction F3 recovered during the desorption step D2 of the processaccording to the invention optionally containing the DCE formed in thechlorination reactor R2 and extracted in the desorption step, after anoptional treatment making it possible to reduce the concentration, infraction F3, of the compounds that are heavier than ethane as explainedbelow, optionally with the addition of fresh washing agent.

Preferably, the washing agent used for the absorption step A is composedof all or part of fraction F3 recovered during the desorption step D2 ofthe process according to the invention optionally containing the DCEformed in the chlorination reactor and extracted in the desorption step,after the abovementioned optional treatment, optionally with theaddition of fresh washing agent. In a particularly preferred manner, thewashing agent used for the absorption step A is composed of all or partof fraction F3 recovered during the desorption step D2 of the processaccording to the invention, after the aforementioned optional treatment,with the addition of fresh washing agent (to compensate for losses ofwashing agent during the absorption and desorption steps).

The abovementioned optional additional treatment making it possible toreduce the concentration, in fraction F3, of the compounds that areheavier than ethane, preferably of the compounds comprising at least 3carbon atoms, may be a step of desorbing the compounds that are heavierthan ethane and lighter than fraction F3 or a step of distillingfraction F3. Preferably, it consists of desorbing the compounds that areheavier than ethane and lighter than fraction F3. Preferably, thistreatment of fraction F3 takes place.

An essential advantage lies in the fact that the presence of this DCE isnot at all troublesome, as it is the compound mainly formed during theoxychlorination or chlorination.

The ratio between the respective throughputs of washing agent and of gasmixture supplied to the absorption A is not critical and can vary to alarge extent. It is in practice limited only by the cost of regeneratingthe washing agent. In general, the throughput of washing agent is atleast 1, preferably at least 5 and particularly preferably at least 10tonnes per tonne of the gas mixture supplied to the absorption. Ingeneral, the throughput of washing agent is at most 100, preferably atmost 50 and particularly preferably at most 25 tonnes per tonne ofethylene and ethane to be extracted from the gas mixture supplied to theabsorption.

The absorption step A is advantageously carried out by means of anabsorber such as, for example, a climbing film or falling film absorberor an absorption column chosen from plate columns, columns with randompacking, columns with structured packing, columns combining one or moreof the aforementioned internals and spray columns. The absorption step Ais preferably carried out using an absorption column and particularlypreferably using a plate absorption column. The absorption column isadvantageously equipped with associated accessories such as, forexample, at least one condenser or chiller that is internal or externalto the column.

The abovementioned absorption step A is advantageously carried out at apressure of at least 15, preferably of at least 20 and particularlypreferably of at least 25 bar absolute. The absorption step A isadvantageously carried out at a pressure of at most 40, preferably of atmost 35 and particularly preferably of at most 30 bar absolute.

The temperature at which the absorption step A is carried out isadvantageously at least −10, preferably at least 0 and particularlypreferably at least 10° C. at the top of the absorber or absorptioncolumn. It is advantageously at most 60, preferably at most 50 andparticularly preferably at most 40° C. at the top of the absorber orabsorption column.

The temperature at the bottom of the absorber or absorption column is atleast 0, preferably at least 10 and particularly preferably at least 20°C. It is advantageously at most 70, preferably at most 60 andparticularly preferably at most 50° C.

Step c) of absorption A consists of separating said gas mixture into afraction enriched with the compounds that are lighter than ethylenecontaining some of the ethylene (fraction A) and into a fraction F1.

Fraction A is enriched with the compounds that are lighter thanethylene. These compounds are generally methane, nitrogen, oxygen,hydrogen and carbon monoxide.

Advantageously, fraction A contains at least 70%, preferably at least80% and particularly preferably at least 85% by weight of the compoundsthat are lighter than ethylene contained in the dry gas mixture.Advantageously, fraction A contains at most 99.99%, preferably at most99.95% and particularly preferably at most 99.9% by weight of thecompounds that are lighter than ethylene contained in the dry gasmixture.

Fraction A is characterized by an acetylene content that isadvantageously less than or equal to 0.01%, preferably less than orequal to 0.005% and particularly preferably less than or equal to 0.001%by volume relative to the total volume of fraction A.

Advantageously, fraction A contains at most 1%, preferably at most 0.5%and particularly preferably at most 0.2% of ethane relative to the totalvolume of fraction A.

Fraction A is characterized by a content of compounds comprising atleast 3 carbon atoms that is advantageously less than or equal to 0.01%,preferably less than or equal to 0.005% and particularly preferably lessthan or equal to 0.001% by volume relative to the total volume offraction A.

Fraction A is characterized by a content of sulfur compounds that isadvantageously less than or equal to 0.01%, preferably less than orequal to 0.005% and particularly preferably less than or equal to 0.001%by volume relative to the total volume of fraction A.

Fraction A contains at least 3%, preferably at least 4% and particularlypreferably at least 5% of the ethylene contained in the dry gas mixture.

Advantageously, fraction F1 contains at most 30%, preferably at most 20%and particularly preferably at most 15% by weight of the compounds thatare lighter than ethylene contained in the dry gas mixture.

Fraction F1 advantageously contains at least 0.1%, preferably at least0.3% and particularly preferably at least 0.5% by weight of ethylenerelative to the total weight of fraction F1. Fraction F1 preferablycontains at most 20%, preferably at most 15% and particularly preferablyat most 12% by weight of ethylene relative to the total weight offraction F1.

Fraction F1 advantageously contains at least 0.3%, preferably at least0.8% and particularly preferably at least 1% by weight of ethanerelative to the total weight of fraction F1. Fraction F1 advantageouslycontains at most 25%, preferably at most 20%, particularly preferably atmost 18% by weight of ethane relative to the total weight of fractionF1.

Fraction F1 is characterized, in addition, by an acetylene content thatis advantageously less than or equal to 0.1%, preferably less than orequal to 0.05% and particularly preferably less than or equal to 0.01%by weight relative to the total weight of fraction F1.

Fraction F1 is characterized by a content of compounds comprising atleast 3 carbon atoms that is advantageously less than or equal to 1%,preferably less than or equal to 0.5% and particularly preferably lessthan or equal to 0.1% by weight relative to the total weight of fractionF1.

Fraction F1 is characterized by a content of sulfur compounds that isadvantageously less than or equal to 0.005%, preferably less than orequal to 0.002% and particularly preferably less than or equal to 0.001%by weight relative to the total weight of fraction F1.

According to step d) of the process according to the invention, fractionA is conveyed to a chlorination reactor R1 in which most of the ethylenepresent in fraction A is converted into 1,2-dichloroethane and the1,2-dichloroethane obtained is separated from the stream of productsderived from the chlorination reactor R1.

The chlorination reaction is advantageously carried out in a liquidphase (preferably mainly DCE) containing a dissolved catalyst such asFeCl₃ or another Lewis acid. It is possible to advantageously combinethis catalyst with cocatalysts such as alkali metal chlorides. A pairwhich has given good results is the complex of FeCl₃ with LiCl (lithiumtetrachloroferrate—as described in Patent Application NL 6901398).

The amounts of FeCl₃ advantageously used are around 1 to 30 g of FeCl₃per kg of liquid stock. The molar ratio of FeCl₃ to LiCl isadvantageously around 0.5 to 2.

In addition, the chlorination process is preferably performed in achlorinated organic liquid medium. More preferably, this chlorinatedorganic liquid medium, also called liquid stock, is mainly composed ofDCE.

The chlorination process according to the invention is advantageouslycarried out at temperatures between 30 and 150° C. Good results havebeen obtained regardless of the pressure both at a temperature below theboiling point (chlorination under subcooled conditions) and at theboiling point itself (chlorination on boiling).

When the chlorination process according to the invention is achlorination process under subcooled conditions, it gave good results byoperating at a temperature which was advantageously greater than orequal to 50° C. and preferably greater than or equal to 60° C., butadvantageously less than or equal to 80° C. and preferably less than orequal to 70° C., and with a pressure in the gas phase advantageouslygreater than or equal to 1 and preferably greater than or equal to 1.1bar absolute, but advantageously less than or equal to 30, preferablyless than or equal to 25 and particularly preferably less than or equalto 20 bar absolute.

A process for chlorination at boiling point is particularly preferred,which makes it possible, where appropriate, to usefully recover the heatof reaction. In this case, the reaction advantageously takes place at atemperature greater than or equal to 60° C., preferably greater than orequal to 70° C. and particularly preferably greater than or equal to 85°C., but advantageously less than or equal to 150° C. and preferably lessthan or equal to 135° C., and with a pressure in the gas phaseadvantageously greater than or equal to 0.2, preferably greater than orequal to 0.5, particularly preferably greater than or equal to 1.1 andmost particularly preferably greater than or equal to 1.3 bar absolute,but advantageously less than or equal to 20 and preferably less than orequal to 15 bar absolute.

The chlorination process may also be a hybrid loop-cooled process forchlorination at boiling point. The expression “hybrid loop-cooledprocess for chlorination at boiling point” is understood to mean aprocess in which cooling of the reaction medium is carried out, forexample by means of an exchanger immersed in the reaction medium or by aloop circulating in an exchanger, while producing in the gaseous phaseat least the amount of DCE formed. Advantageously, the reactiontemperature and pressure are adjusted for the DCE produced to exit inthe gas phase and for the remainder of the heat from the reaction mediumto be removed by means of the exchange surface.

Fraction A containing the ethylene and also the chlorine (itself pure ordiluted) may be introduced, together or separately, into the reactionmedium by any known device. A separate introduction of fraction A may beadvantageous in order to increase its partial pressure and to facilitateits dissolution which often constitutes a limiting step of the process.

The chlorine is added in a sufficient amount to convert most of theethylene and without requiring the addition of an excess of unconvertedchlorine. The chlorine/ethylene ratio used is preferably between 1.2 and0.8 and particularly preferably between 1.05 and 0.95 mol/mol.

The chlorinated products obtained mainly contain DCE and also smallamounts of by-products such as 1,1,2-trichloroethane or small amounts ofethane or methane chlorination products.

The separation of the DCE obtained from the stream of products derivedfrom the chlorination reactor R1 is carried out according to knownmethods and makes it possible in general to exploit the heat of thechlorination reaction. It is then preferably carried out by condensationand gas/liquid separation.

According to step e) of the process according to the invention, fractionF1 is subjected to a desorption D1 which consists of separating fractionF1 into an ethylene fraction depleted of the compounds that are lighterthan ethylene (fraction C) which is conveyed to a chlorination reactorR2, the stream of products derived from this reactor being added to thedry gas mixture subjected to step c) after having optionally extractedthe 1,2-dichloroethane formed, and into a fraction F2.

The desorption step D1 is advantageously a desorption step in whichfraction C is extracted from fraction F1.

The washing agent recovered after desorption step D1, the fraction F2,is sent to the second desorption step D2.

The desorption step D1 is advantageously carried out by means of adesorber such as, for example, a climbing film or falling film desorber,a reboiler or a desorption column chosen from plate columns, columnswith random packing, columns with structured packing, columns combiningone or more of the aforementioned internals and spray columns. Thedesorption step D1 is preferably carried out by means of a desorptioncolumn and particularly preferably by means of a plate desorptioncolumn.

The desorption column is advantageously equipped with associatedaccessories such as, for example, at least one condenser or one chillerthat is internal or external to the column and at least one reboiler.

The desorption step D1 is advantageously carried out at a pressure of atleast 1, preferably at least 2 and particularly preferably at least 3bar absolute. The desorption step D1 is advantageously carried out at apressure of at most 20, preferably at most 15 and particularlypreferably at most 10 bar absolute.

The temperature at which the desorption step D1 is carried out isadvantageously chosen so that more than 80%, preferably more than 90% ofthe ethane contained in fraction F1 are found in fraction F2. Thetemperature at which the desorption step D1 is carried out isadvantageously at least −10, preferably at least 0 and particularlypreferably at least 10° C. at the top of the desorber or desorptioncolumn. It is advantageously at most 60, preferably at most 50 andparticularly preferably at most 40° C. at the top of the desorber ordesorption column.

The temperature at the bottom of the desorber or desorption column is atleast 60, preferably at least 80 and particularly preferably at least100° C. It is advantageously at most 200, preferably at most 160 andparticularly preferably at most 150° C.

Step e) of desorption D1 is advantageously a desorption step in which anethylene fraction depleted of the compounds that are lighter thanethylene (fraction C) is extracted from fraction F1.

Advantageously, fraction C contains at least 80%, preferably at least90% and particularly preferably at least 95% by weight of the compoundsthat are lighter than ethylene contained in fraction F1.

Fraction C is characterized by an acetylene content that isadvantageously less than or equal to 0.01%, preferably less than orequal to 0.005% and particularly preferably less than or equal to 0.001%by volume relative to the total volume of fraction C.

Fraction C is characterized by a content of compounds comprising atleast 3 carbon atoms that is advantageously less than or equal to 0.01%,preferably less than or equal to 0.005% and particularly preferably lessthan or equal to 0.001% by volume relative to the total volume offraction C.

Fraction C is characterized by a content of sulfur compounds that isadvantageously less than or equal to 0.01%, preferably less than orequal to 0.005% and particularly preferably less than or equal to 0.001%by volume relative to the total volume of fraction C.

Fraction C contains at least 10%, preferably at least 15% andparticularly preferably at least 20% of the ethylene contained infraction F1. Fraction C advantageously contains at most 80%, preferablyat most 70% and particularly preferably at most 65% of the ethylenecontained in fraction F1.

Fraction C is then conveyed to the chlorination reactor R2.

The chlorination reaction is advantageously carried out in a liquidphase (preferably mainly DCE) containing a dissolved catalyst such asFeCl₃ or another Lewis acid. It is possible to advantageously combinethis catalyst with cocatalysts such as alkali metal chlorides. A pairwhich has given good results is the complex of FeCl₃ with LiCl (lithiumtetrachloroferrate—as described in Patent Application NL 6901398).

The amounts of FeCl₃ advantageously used are around 1 to 10 g of FeCl₃per kg of liquid stock. The molar ratio of FeCl₃ to LiCl isadvantageously around 0.5 to 2.

The chlorination process according to the invention is advantageouslycarried out at temperatures between 30 and 150° C. Good results havebeen obtained regardless of the pressure both at a temperature below theboiling point (chlorination under subcooled conditions) and at theboiling point itself (chlorination on boiling).

When the chlorination process according to the invention is achlorination process under subcooled conditions, it gave good results byoperating at a temperature which was advantageously greater than orequal to 50° C. and preferably greater than or equal to 60° C., butadvantageously less than or equal to 80° C. and preferably less than orequal to 70° C., and with a pressure in the gas phase advantageouslygreater than or equal to 1.5 and preferably greater than or equal to 2bar absolute, but advantageously less than or equal to 20, preferablyless than or equal to 10 and particularly preferably less than or equalto 6 bar absolute.

A process for chlorination at boiling point is particularly preferred,which makes it possible, where appropriate, to usefully recover the heatof reaction. In this case, the reaction advantageously takes place at atemperature greater than or equal to 60° C., preferably greater than orequal to 90° C. and particularly preferably greater than or equal to 95°C., but advantageously less than or equal to 150° C. and preferably lessthan or equal to 135° C., and with a pressure in the gas phaseadvantageously greater than or equal to 0.2, preferably greater than orequal to 0.5, particularly preferably greater than or equal to 1.2 andmost particularly preferably greater than or equal to 1.5 bar absolute,but advantageously less than or equal to 10 and preferably less than orequal to 6 bar absolute.

The chlorination process may also be a hybrid shuttle-cooled process forchlorination at boiling point. The expression “hybrid shuttle-cooledprocess for chlorination at boiling point” is understood to mean aprocess in which cooling of the reaction medium is carried out, forexample by means of an exchanger immersed in the reaction medium or by ashuttle circulating in an exchanger, while producing in the gaseousphase at least the amount of DCE formed. Advantageously, the reactiontemperature and pressure are adjusted for the DCE produced to exit inthe gas phase and for the remainder of the heat from the reaction mediumto be removed by means of the exchange surface.

In addition, the chlorination process is advantageously performed in achlorinated organic liquid medium. Preferably, this chlorinated organicliquid medium, also called liquid stock, is mainly composed of DCE.

Fraction A containing the ethylene and also the chlorine (itself pure ordiluted) may be introduced, together or separately, into the reactionmedium by any known device. A separate introduction of fraction A may beadvantageous in order to increase its partial pressure and to facilitateits dissolution which often constitutes a limiting step of the process.

The chlorine is added in a sufficient amount to convert most of theethylene and without requiring the addition of an excess of unconvertedchlorine. The chlorine/ethylene ratio used is preferably between 1.2 and0.8 and particularly preferably between 1.05 and 0.95 mol/mol.

The chlorinated products obtained mainly contain DCE and also smallamounts of by-products such as 1,1,2-trichloroethane or small amounts ofethane or methane chlorination products.

The separation of the DCE obtained from the stream of products derivedfrom the chlorination reactor R2 is optional. In certain cases it may beadvantageous not to isolate the DCE formed in the chlorination reactorfrom the stream of products derived from the chlorination reactor.Preferably however, the DCE formed in the chlorination reactor isisolated from the stream of products derived from the chlorinationreactor R2.

When it takes place, the separation of the DCE obtained from the streamof products derived from the chlorination reactor is carried outaccording to known methods and in general makes it possible to exploitthe heat of the chlorination reaction. It is then preferably carried outby condensation and gas/liquid separation.

Advantageously, fraction F2 contains at most 3%, preferably at most 1%and particularly preferably at most 0.5% of the compounds that arelighter than ethylene contained in the gas supplied to the desorption.

Fraction F2 advantageously contains at least 0.1%, preferably at least0.3% and particularly preferably at least 0.5% by weight of ethylenerelative to the total weight of fraction F2. Fraction F2 preferablycontains at most 20%, preferably at most 15% and particularly preferablyat most 12% by weight of ethylene relative to the total weight offraction F2.

Fraction F2 advantageously contains at least 0.3%, preferably at least0.8% and particularly preferably at least 1% by weight of ethanerelative to the total weight of fraction F2. Fraction F2 advantageouslycontains at most 25%, preferably at most 20%, particularly preferably atmost 18% by weight of ethane relative to the total weight of fractionF2.

Fraction F2 is characterized, in addition, by an acetylene content thatis advantageously less than or equal to 0.1%, preferably less than orequal to 0.05% and particularly preferably less than or equal to 0.01%by weight relative to the total weight of fraction F2.

Fraction F2 is characterized by a content of compounds comprising atleast 3 carbon atoms that is advantageously less than or equal to 1%,preferably less than or equal to 0.5% and particularly preferably lessthan or equal to 0.1% by weight relative to the total weight of fractionF2.

Fraction F2 is characterized by a content of sulfur compounds that isadvantageously less than or equal to 0.005%, preferably less than orequal to 0.002% and particularly preferably less than or equal to 0.001%by weight relative to the total weight of fraction F2.

According to step f) of the process according to the invention, fractionF2 is subjected to a desorption D2 which consists of separating fractionF2 into a fraction enriched with ethylene (fraction B) and into afraction F3, optionally containing the 1,2-dichloroethane formed in thechlorination reactor R2 then extracted, if it has not previously beenextracted, which is recycled to the absorption A, optionally after anadditional treatment intended to reduce the concentration, in fractionF3, of the compounds that are heavier than ethane.

The desorption step D2 is advantageously a desorption step in whichfraction B is extracted from the washing agent.

The washing agent recovered after the desorption step D2, optionallycontaining the DCE formed in the chlorination reactor R2 then extracted,may be removed, completely or partly conveyed to the oxychlorinationsector where the DCE comes together with the DCE formed in theoxychlorination reactor, or completely or partly reconveyed to theabsorption step of the process according to the invention, optionallyafter the previously mentioned treatment (step c)), with the optionaladdition of fresh washing agent. Preferably, the washing agent recoveredafter the desorption step D2 is reconveyed to the absorption step of theprocess according to the invention, after the abovementioned optionaltreatment, with optional addition of fresh washing agent, or to theoxychlorination sector. In the case where the DCE formed in thechlorination reactor R2 is isolated from the stream of products derivedfrom the chlorination reactor at the chlorination outlet, in aparticularly preferred manner, the washing agent recovered after thedesorption step D2 is completely or partly reconveyed to the absorptionstep of the process according to the invention, after the abovementionedoptional treatment, with addition of fresh washing agent.

The desorption step D2 is advantageously carried out by means of adesorber such as, for example, a climbing film or falling film desorber,a reboiler or a desorption column chosen from plate columns, columnswith random packing, columns with structured packing, columns combiningone or more of the aforementioned internals and spray columns. Thedesorption step D2 is preferably carried out by means of a desorptioncolumn and particularly preferably by means of a plate desorptioncolumn.

The desorption column is advantageously equipped with associatedaccessories such as, for example, at least one condenser or one chillerthat is internal or external to the column and at least one reboiler.

The desorption step D2 is advantageously carried out at a pressure of atleast 1, preferably at least 2 and particularly preferably at least 3bar absolute. The desorption step D2 is advantageously carried out at apressure of at most 20, preferably at most 15 and particularlypreferably at most 10 bar absolute.

The temperature at which the desorption step D2 is carried out isadvantageously chosen so that more than 90%, preferably more than 95% ofthe ethane contained in fraction F1 is found in fraction B. Thetemperature at which the desorption step D2 is carried out isadvantageously at least −10, preferably at least 0 and particularlypreferably at least 10° C. at the top of the desorber or desorptioncolumn. It is advantageously at most 60, preferably at most 50 andparticularly preferably at most 40° C. at the top of the desorber ordesorption column.

The temperature at the bottom of the desorber or desorption column is atleast 60, preferably at least 80 and particularly preferably at least100° C. It is advantageously at most 200, preferably at most 160 andparticularly preferably at most 150° C.

Step f) of desorption D2 consists of separating fraction F2 into afraction enriched with ethylene (fraction B) and into a fraction F3,optionally containing the DCE formed in the chlorination reactor R2 thenextracted, if it has not previously been extracted, which is recycled tothe absorption A, optionally after an additional treatment intended toremove the compounds that are heavier than ethane.

Fraction B is enriched with ethylene.

Advantageously, fraction B contains at most 1%, preferably at most 0.5%and particularly preferably at most 0.2% by volume of hydrogen relativeto the total volume of fraction B.

Fraction B is characterized by an ethylene content that isadvantageously greater than or equal to 2%, preferably greater than orequal to 3% and particularly preferably greater than or equal to 4% byvolume relative to the total volume of fraction B.

Fraction B is characterized by an ethane content that is advantageouslyless than or equal to 98%, preferably less than or equal to 97% andparticularly preferably less than or equal to 96% by volume relative tothe total volume of fraction B.

Fraction B advantageously contains at most 0.01%, preferably at most0.005% and particularly preferably at most 0.001% of compoundscomprising at least 3 carbon atoms relative to the total volume offraction B.

Fraction B is characterized, in addition, by an acetylene content thatis advantageously less than or equal to 0.1%, preferably less than orequal to 0.05% and particularly preferably less than or equal to 0.01%by volume relative to the total volume of fraction B.

Fraction B is characterized by a content of sulfur compounds that isadvantageously less than or equal to 0.005%, preferably less than orequal to 0.002% and particularly preferably less than or equal to 0.001%by volume relative to the total volume of fraction B.

Advantageously, fraction F3 contains at least 80%, preferably at least85% and particularly preferably at least 90% by weight of the compoundsthat are heavier than ethane contained in fraction F2.

Advantageously, fraction F3 contains at most 0.5%, preferably at most0.3% and particularly preferably at most 0.1% by weight of ethanerelative to the total weight of fraction F3.

Advantageously, fraction F3 contains at most 0.3%, preferably at most0.1% and particularly preferably at most 0.05% by weight of ethylenerelative to the total weight of fraction F3.

According to step g) of the process according to the invention, fractionB is conveyed to an oxychlorination reactor in which most of theethylene present in fraction B is converted into 1,2-dichloroethane, the1,2-dichloroethane obtained is separated from the stream of productsderived from the oxychlorination reactor and is optionally added to the1,2-dichloroethane formed in the chlorination reactor R1 and optionallyto that formed in the chlorination reactor R2.

The oxychlorination reaction is advantageously carried out in thepresence of a catalyst comprising active elements, including copper,deposited on an inert support. The inert support is advantageouslychosen from alumina, silica gels, mixed oxides, clays and other supportsof natural origin. Alumina constitutes a preferred inert support.

Catalysts comprising active elements which are advantageously at least 2in number, one of which is copper, are preferred. Among the activeelements other than copper, mention may be made of alkali metals,alkaline-earth metals, rare-earth metals and metals from the groupcomposed of ruthenium, rhodium, palladium, osmium, iridium, platinum andgold. The catalysts containing the following active elements areparticularly advantageous: copper/magnesium/potassium,copper/magnesium/sodium, copper/magnesium/lithium,copper/magnesium/caesium, copper/magnesium/sodium/lithium,copper/magnesium/potassium/lithium and copper/magnesium/caesium/lithium,copper/magnesium/sodium/potassium, copper/magnesium/sodium/caesium andcopper/magnesium/potassium/caesium. The catalysts described in PatentApplications EP-A 255 156, EP-A 494 474, EP-A 657 212 and EP-A 657 213,incorporated by reference, are most particularly preferred.

The copper content, calculated in metal form, is advantageously between30 and 90 g/kg, preferably between 40 and 80 g/kg and particularlypreferably between 50 and 70 g/kg of the catalyst.

The magnesium content, calculated in metal form, is advantageouslybetween 10 and 30 g/kg, preferably between 12 and 25 g/kg andparticularly preferably between 15 and 20 g/kg of the catalyst.

The alkali metal content, calculated in metal form, is advantageouslybetween 0.1 and 30 g/kg, preferably between 0.5 and 20 g/kg andparticularly preferably between 1 and 15 g/kg of the catalyst.

The Cu/Mg/alkali metal(s) atomic ratios are advantageously1/0.1-2/0.05-2, preferably 1/0.2-1.5/0.1-1.5 and particularly preferably1/0.5-1/0.15-1.

Catalysts having a specific surface area measured according to the BETmethod with nitrogen advantageously comprise between 25 m²/g and 300m²/g, preferably between 50 and 200 m²/g and particularly preferablybetween 75 and 175 m²/g, are particularly advantageous.

The catalyst may be used in a fixed bed or in a fluidized bed. Thissecond option is preferred. The oxychlorination process is operatedunder the range of conditions usually recommended for this reaction. Thetemperature is advantageously between 150 and 300° C., preferablybetween 200 and 275° C. and most preferably from 215 to 255° C. Thepressure is advantageously greater than atmospheric pressure. Valuesbetween 2 and 10 bar absolute have given good results. The range between4 and 7 bar absolute is preferred. This pressure may usefully beadjusted to attain an optimum residence time in the reactor and to keepa constant rate of passage for various speeds of operation. The usualresidence times range from 1 to 60 s and preferably from 10 to 40 s.

The source of oxygen for this oxychlorination may be air, pure oxygen ora mixture thereof, preferably pure oxygen. The latter solution, whichallows easy recycling of the unconverted reactants, is preferred.

The reactants may be introduced into the bed by any known device. It isgenerally advantageous to introduce the oxygen separately from the otherreactants for safety reasons. These safety reasons also require keepingthe gas mixture leaving the reactor or recycled thereto outside thelimits of inflammability at the pressures and temperatures in question.It is preferable to maintain a so-called rich mixture, that is to saycontaining too little oxygen relative to the fuel to ignite. In thisregard, the abundant presence (>2 vol %, preferably >5 vol %) ofhydrogen would constitute a disadvantage given the wide inflammabilityrange of this compound.

The hydrogen chloride/oxygen ratio used is advantageously between 3 and6 mol/mol. The ethylene/hydrogen chloride ratio is advantageouslybetween 0.4 and 0.6 mol/mol.

The chlorinated products obtained mainly contain DCE and also smallamounts of by-products such as 1,1,2-trichloroethane.

According to step g) of the process according to the invention, the DCEobtained is separated from the stream of products derived from theoxychlorination reactor and is optionally added to the DCE formed in thechlorination reactor R1 and optionally to the DCE formed in thechlorination reactor R2.

The separation of the DCE obtained from the stream of products derivedfrom the oxychlorination reactor is carried out according to knownmethods. It is preferably carried out first by condensation. The heat ofthe oxychlorination reaction is generally recovered in the vapour statewhich may be used for the separations or for any other use.

After exiting from the oxychlorination reactor, the stream of productsderived from the reactor, from which the DCE has been extracted, is alsoadvantageously washed to recover the unconverted HCl. This washingoperation is advantageously an alkaline washing step. It is preferablyfollowed by a gas/liquid separation step which makes it possible torecover the DCE formed in liquid form and finally to dry the DCE. Thegases optionally recycled to the ODH are dried by cooling.

The expression “is optionally added to the DCE formed in thechlorination reactor R1” is understood to mean that the DCE formed inthe chlorination reactor R1 and isolated from the stream of productsderived from this reactor may or may not be mixed with the DCE formed inthe oxychlorination reactor. Preferably, it is added thereto.

The expression “is optionally added to the DCE formed in thechlorination reactor R2” is understood to mean that if the DCE formed inthe chlorination reactor R2 is isolated from the stream of productsderived from this reactor, on exiting the chlorination reactor or afterthe desorption step D2, the DCE formed in the oxychlorination reactormay or may not be added thereto. Preferably, it is added thereto.

According to optional step h) of the process according to the invention,the stream of products derived from the oxychlorination reactor, fromwhich the DCE has been extracted, optionally containing an additionalstream of ethane previously introduced into one of steps b) to g), isoptionally recycled to step a) after having been optionally purged ofgases and/or after an optional additional treatment in order toeliminate the chlorinated products contained therein.

The stream of products derived from the oxychlorination reactor, fromwhich the DCE has been extracted, may be recycled to step a) or not,during optional step h). Preferably, the stream of products derived fromthe oxychlorination reactor, from which the DCE has been extracted, isrecycled to step a) during step h).

An additional stream of ethane introduced previously into one of stepsb) to g) may therefore be found in this stream recycled in step h).

Thus, in the particular case where only a lean ethane stream, forexample having 30 or 40 vol % of ethane, is available, it isadvantageous to introduce this stream not into step a) directly but, forexample, into the absorption/desorption step e′) so that the light gasesare extracted therefrom and the residual stream is recycled to the ODHduring step h).

Similarly, in the particular case where the stream of ethane availableis rich in sulfur compounds, it may be advantageous to introduce thisstream not into step a) directly but, for example, into step b) toremove these troublesome compounds therefrom; after having undergonesteps c) to g), this stream of ethane is then recycled to the ODH duringstep h).

The stream of products derived from the oxychlorination reactor, fromwhich the DCE has been extracted, is advantageously characterized by anethane content that is greater than or equal to 10%, preferably greaterthan or equal to 20%, particularly preferably greater than or equal to30% and most particularly preferably greater than or equal to 40% byvolume relative to the total volume of said stream.

The stream of products derived from the oxychlorination reactor, fromwhich the DCE has been extracted, is advantageously characterized by anethane content that is less than or equal to 90%, preferably less thanor equal to 85%, and particularly preferably less than or equal to 80%by volume relative to the total volume of said stream.

The stream of products derived from the oxychlorination reactor, fromwhich the DCE has been extracted, is advantageously characterized by anethylene content that is less than or equal to 10%, preferably less thanor equal to 5% and particularly preferably less than or equal to 2% byvolume relative to the total volume of said stream.

The stream of products derived from the oxychlorination reactor, fromwhich the DCE has been extracted, is advantageously characterized by ahydrogen content that is less than or equal to 10%, preferably less thanor equal to 5% and particularly preferably less than or equal to 2% byvolume relative to the total volume of said stream.

The stream of products derived from the oxychlorination reactor, fromwhich the DCE has been extracted, is advantageously characterized by acarbon monoxide content that is less than or equal to 20%, preferablyless than or equal to 15% and particularly preferably less than or equalto 10% by volume relative to the total volume of said stream.

The stream of products derived from the oxychlorination reactor, fromwhich the DCE has been extracted, is advantageously characterized by acarbon dioxide content that is less than or equal to 40%, preferablyless than or equal to 35% and particularly preferably less than or equalto 30% by volume relative to the total volume of said stream.

The stream of products derived from the oxychlorination reactor, fromwhich the DCE has been extracted, is advantageously characterized by anoxygen content that is less than or equal to 10%, preferably less thanor equal to 5% and particularly preferably less than or equal to 3% byvolume relative to the total volume of said stream.

According to step h) of the preferred process according to theinvention, the stream of products derived from the oxychlorinationreactor, from which the DCE has been extracted, optionally containing anadditional stream of ethane previously introduced into one of steps b)to g), is recycled to step a).

The recycling to step a) is in this case performed after an optionalpurge of gases and/or after an optional additional treatment in order toeliminate the chlorinated products (notably traces of DCE and/or ofother chlorinated products such as ethylene chloride) contained in theconsidered stream of products. The additional treatment when it takesplace, may be performed by using active carbon or an adsorbent.

Either the purge of gases or the additional treatment or both of themmay be performed. More preferably, the stream of products is recycled tostep a) without being purged of gases and without any additionaltreatment in order to eliminate the chlorinated products contained in.

Indeed, the recycling of this stream of products to the ODH step a) maybe interesting to benefit from the favourable catalytic effect of thechlorinated products on the ODH reaction.

The DCE obtained by chlorination and by oxychlorination of ethylene maythen be converted into VC.

The invention therefore also relates to a process for the manufacture ofVC. To this effect, the invention relates to a process for themanufacture of VC characterized in that:

-   a) a stream of ethane is subjected to a catalytic oxydehydrogenation    producing a gas mixture containing ethylene, unconverted ethane,    water and secondary constituents;-   b) said gas mixture is optionally washed and dried thus producing a    dry gas mixture;-   c) after an optional additional purification step, said dry gas    mixture comprising the stream of products derived from the    chlorination reactor R2 separated in step e) is subjected to an    absorption A which consists of separating said gas mixture into a    fraction enriched with the compounds that are lighter than ethylene    containing some of the ethylene (fraction A) and into a fraction F1;-   d) fraction A is conveyed to a chlorination reactor R1 in which most    of the ethylene present in fraction A is converted into    1,2-dichloroethane and the 1,2-dichloroethane obtained is separated    from the stream of products derived from the chlorination reactor    R1;-   e) fraction F1 is subjected to a desorption D1 which consists of    separating fraction F1 into an ethylene fraction depleted of the    compounds that are lighter than ethylene (fraction C) which is    conveyed to a chlorination reactor R2, the stream of products    derived from this reactor being added to the dry gas mixture    subjected to step c) after having optionally extracted the    1,2-dichloroethane formed, and into a fraction F2;-   f) fraction F2 is subjected to a desorption D2 which consists of    separating fraction F2 into a fraction enriched with ethylene    (fraction B) and into a fraction F3, optionally containing the    1,2-dichloroethane formed in the chlorination reactor R2 then    extracted, if it has not previously been extracted, which is    recycled to the absorption A, optionally after an additional    treatment intended to reduce the concentration, in fraction F3, of    the compounds that are heavier than ethane;-   g) fraction B is conveyed to an oxychlorination reactor in which    most of the ethylene present in fraction B is converted into    1,2-dichloroethane, the 1,2-dichloroethane obtained is separated    from the stream of products derived from the oxychlorination reactor    and is optionally added to the 1,2-dichloroethane formed in the    chlorination reactor R1 and optionally to that formed in the    chlorination reactor R2; and-   h) the stream of products derived from the oxychlorination reactor,    from which the 1,2-dichloroethane has been extracted, optionally    containing an additional stream of ethane previously introduced in    one of steps b) to g), is optionally recycled to step a) after    having been optionally purged of gases and/or after an optional    additional treatment in order to eliminate the chlorinated products    contained therein;-   i) the 1,2-dichloroethane obtained is subjected to a pyrolysis thus    producing VC.

The particular conditions and preferences defined for the process forthe manufacture of DCE according to the invention apply to the processfor the manufacture of VC according to the invention.

The conditions under which the pyrolysis may be carried out are known toa person skilled in the art. This pyrolysis is advantageously achievedby a reaction in the gas phase in a tube furnace. The usual pyrolysistemperatures extend between 400 and 600° C. with a preference for therange between 480° C. and 540° C. The residence time is advantageouslybetween 1 and 60 seconds with a preference for the range of 5 to 25seconds. The conversion rate of the DCE is advantageously limited to 45to 75% in order to limit the formation of by-products and fouling of thefurnace pipes. The following steps make it possible, using any knowndevice, to collect the purified VC and the hydrogen chloride to beupgraded preferably in the oxychlorination. Following purification, theunconverted DCE is advantageously reconveyed to the pyrolysis furnace.

In addition, the invention also relates to a process for the manufactureof PVC. To this effect, the invention relates to a process for themanufacture of PVC characterized in that:

-   a) a stream of ethane is subjected to a catalytic oxydehydrogenation    producing a gas mixture containing ethylene, unconverted ethane,    water and secondary constituents;-   b) said gas mixture is optionally washed and dried thus producing a    dry gas mixture;-   c) after an optional additional purification step, said dry gas    mixture comprising the stream of products derived from the    chlorination reactor R2 separated in step e) is subjected to an    absorption A which consists of separating said gas mixture into a    fraction enriched with the compounds that are lighter than ethylene    containing some of the ethylene (fraction A) and into a fraction F1;-   d) fraction A is conveyed to a chlorination reactor R1 in which most    of the ethylene present in fraction A is converted into    1,2-dichloroethane and the 1,2-dichloroethane obtained is separated    from the stream of products derived from the chlorination reactor    R1;-   e) fraction F1 is subjected to a desorption D1 which consists of    separating fraction F1 into an ethylene fraction depleted of the    compounds that are lighter than ethylene (fraction C) which is    conveyed to a chlorination reactor R2, the stream of products    derived from this reactor being added to the dry gas mixture    subjected to step c) after having optionally extracted the    1,2-dichloroethane formed, and into a fraction F2;-   f) fraction F2 is subjected to a desorption D2 which consists of    separating fraction F2 into a fraction enriched with ethylene    (fraction B) and into a fraction F3, optionally containing the    1,2-dichloroethane formed in the chlorination reactor R2 then    extracted, if it has not previously been extracted, which is    recycled to the absorption A, optionally after an additional    treatment intended to reduce the concentration, in fraction F3, of    the compounds that are heavier than ethane;-   g) fraction B is conveyed to an oxychlorination reactor in which    most of the ethylene present in fraction B is converted into    1,2-dichloroethane, the 1,2-dichloroethane obtained is separated    from the stream of products derived from the oxychlorination reactor    and is optionally added to the 1,2-dichloroethane formed in the    chlorination reactor R1 and optionally to that formed in the    chlorination reactor R2; and-   h) the stream of products derived from the oxychlorination reactor,    from which the 1,2-dichloroethane has been extracted, optionally    containing an additional stream of ethane previously introduced in    one of steps b) to g), is optionally recycled to step a) after    having been optionally purged of gases and/or after an optional    additional treatment in order to eliminate the chlorinated products    contained therein;-   i) the 1,2-dichloroethane obtained is subjected to a pyrolysis thus    producing VC; and-   j) the VC is polymerized to produce PVC.

The particular conditions and preferences defined for the process forthe manufacture of DCE and the process for the manufacture of VCaccording to the invention apply to the process for the manufacture ofPVC according to the invention.

The process for the manufacture of PVC may be a bulk, solution oraqueous dispersion polymerization process, preferably it is an aqueousdispersion polymerization process.

The expression “aqueous dispersion polymerization” is understood to meanradical polymerization in aqueous suspension and also radicalpolymerization in aqueous emulsion and polymerization in aqueousmicrosuspension.

The expression “radical polymerization in aqueous suspension” isunderstood to mean any radical polymerization process performed inaqueous medium in the presence of dispersants and oil-soluble radicalinitiators.

The expression “radical polymerization in aqueous emulsion” isunderstood to mean any radical polymerization process performed inaqueous medium in the presence of emulsifiers and water-soluble radicalinitiators.

The expression “polymerization in aqueous microsuspension”, also calledpolymerization in homogenized aqueous dispersion, is understood to meanany radical polymerization process in which oil-soluble initiators areused and an emulsion of monomer droplets is prepared by virtue of apowerful mechanical stirring and the presence of emulsifiers.

In relation to a similarly simplified thermal cracking process, theprocess according to the invention making use of an ODH step has theadvantage of combining an endothermic step (ethane converted intoethylene) with an exothermic water production step, of taking place at amoderate temperature and of avoiding having to provide the heat ofreaction at a high temperature.

The process according to the invention also has the advantage of makingit possible to recycle the stream of products derived from theoxychlorination, from which the DCE has been extracted, to the ODH step,thus ensuring an increased conversion of ethane into ethylene.Furthermore, given the moderate temperature of the ODH relative tothermal cracking, even if this recycled stream contains traces ofchlorinated organic products such as DCE, their presence does not causematerial behaviour and corrosion problems as occur in the case ofthermal cracking above 800° C. The presence of chlorinated products mayfurthermore be advantageous in so far as it allows an increase of theefficiency of the ODH reaction.

The process according to the invention has the advantage of notgenerating compounds comprising at least 3 carbon atoms in troublesomeamounts, these compounds generally being responsible for a certaininhibition during the pyrolysis of the DCE. This inhibition is due tothe formation of derivatives such as 1,2-dichloropropane andmonochloropropenes. Their aptitude for forming stable allyl radicalsexplains their powerful inhibitory effect on the pyrolysis of DCE whichis carried out by the radical route. The formation of these by-productscontaining 3 carbon atoms and heavier by-products furthermoreconstitutes an unnecessary consumption of reactants in theoxychlorination and in the chlorination, or generates costs fordestroying them. Furthermore, these heavy compounds contribute to thesoiling of the columns and evaporators.

Since the ODH reaction takes place at a lower temperature than thermalcracking, the process according to the invention is advantageouslycharacterized, in addition, by the fact that the formation of heavycompounds by oligomerization is much lower.

The process according to the invention making use of an ODH step alsohas the advantage of limiting the conversion by passing to the ODHwithout having to resort to expensive separations such as those thatrequire an ethylene distillation.

Another advantage of the process according to the invention is that itmakes it possible to have, on the same industrial site, a completelyintegrated process ranging from the hydrocarbon source—namely ethane—upto the polymer obtained starting from the monomer manufactured.

The second variant of the process according to the invention, accordingto which the ODH takes place at temperatures less than or equal to 650°C., has the advantage of generating very small amounts of hydrogen,responsible for numerous drawbacks.

The process according to the invention will now be illustrated withreference to the drawing accompanying the present description. Thisdrawing consists of the appended FIG. 1, schematically representing anembodiment of the process for the manufacture of DCE according to theinvention.

A source of ethane 1 and a source of oxygen 2 are introduced into thereactor 3 in order to be subjected to an ODH therein. The gas mixturecontaining ethylene, unconverted ethane, water and secondaryconstituents 4 produced during the ODH step is subjected to washing anddrying in 5 in order to remove by-products as well as water (6)therefrom. After an optional additional purification step, the dry gasmixture formed 7 to which is added the stream of products 7bis derivedfrom the chlorination sector 23 (known as gas mixture 7ter) is thenconveyed to an absorption column 8 equipped with a condenser. Washingagent from the desorption column 9 is introduced into the absorptioncolumn 8 via the line 10, after having been cooled and repressurizedrespectively in the exchangers 11 and 11′ and the pump 12. Fresh washingagent is added via the line 13 to the washing agent from column 9 and apurge 13bis conveys the washing agent to an additional treatment (notshown) intended to reduce the concentration of the compounds that areheavier than ethane in the washing agent so that it is then reconveyedto the line 10.

After passing into column 8, the gas mixture is separated into thefraction 14 exiting from the top of column 8 and into the fraction 15exiting from the bottom of column 8. Fraction 14, enriched with thecompounds that are lighter than ethylene containing some of theethylene, is conveyed to a chlorination sector 16 comprising thechlorination reactor supplied with chlorine 17 and the equipmentnecessary for the separation of the 1,2-dichloroethane formed 18,particularly by condensation and gas/liquid separation, from the streamof products derived from the chlorination reactor and eliminating theresidual gases 18bis non converted in the chlorination, among whichhydrogen, which may be valorised thermally, chemically or hydraulically.

Fraction 15 comprising DCE enriched with ethylene is then introducedinto the desorption column 19 after having been reheated in theexchanger 20.

After passing into the desorption column 19 equipped with a bottomreboiler and an overhead condenser, fraction 15 is separated intofraction 21 exiting from the top of column 19 and into fraction 22exiting from the bottom of column 19.

Fraction 21 of ethylene depleted of the compounds that are lighter thanethylene is conveyed to a chlorination sector 23 comprising achlorination reactor supplied with chlorine 23bis and the equipmentnecessary for the separation of the 1,2-dichloroethane formed 23ter,particularly by condensation and gas/liquid separation. The stream ofproducts 7bis derived from the chlorination sector is then added to thedry gas mixture 7 to form the gas mixture 7ter.

Fraction 22 is introduced into the desorption column 9 after having beenreheated in the exchanger 11″.

After passing into the desorption column 9 equipped with a bottomreboiler and an overhead condenser, fraction 22 is separated intofraction 24 exiting from the top of column 9 and into fraction 25exiting from the bottom of column 9.

Fraction 24, being characterized by a very low hydrogen content, isconveyed to the ethylene oxychlorination unit 26 supplied with oxygen 27and with hydrogen chloride 28. Fraction 25, mainly containing DCE, isreconveyed to column 8 via the line 10 as explained above. Theexchangers 11 and 11″ are coupled together with a view to saving energy.

The stream of products 30 derived from the oxychlorination reactor isseparated in 26bis in DCE 29 accompanied by liquefied by-products amongwhich water, by condensation followed by washing and gas/liquidseparation. The stream of products 31 derived from the oxychlorinationreactor from which has been extracted the DCE 29 is then recycled to thereactor 3.

The invention claimed is:
 1. A process for the manufacture of 1,2-dichloroethane starting from a stream of ethane, comprising: a) subjecting the stream of ethane to a catalytic oxydehydrogenation thus producing a gas mixture containing ethylene, unconverted ethane, water and secondary constituents; b) drying said gas mixture thus producing a dry gas mixture, wherein said gas mixture is optionally washed before or after said drying; c) after an optional additional purification step, subjecting said dry gas mixture comprising the stream of products derived from the chlorination reactor R2 separated in step e) to an absorption A which consists of separating said gas mixture into a fraction enriched with the compounds that are lighter than ethylene containing some of the ethylene (fraction A) and into a fraction F1; d) conveying said fraction A to a chlorination reactor R1 in which most of the ethylene present in said fraction A is converted into 1,2-dichloroethane, wherein the 1,2-dichloroethane so obtained is separated from the stream of products derived from the chlorination reactor R1; e) subjecting said fraction F1 to a desorption D1 which consists of separating said fraction F1 into an ethylene fraction depleted of the compounds that are lighter than ethylene (fraction C) which is conveyed to a chlorination reactor R2, the stream of products derived from this reactor being added to the dry gas mixture subjected to step c) after having optionally extracted the 1,2-dichloroethane formed, and into a fraction F2; f) subjecting said fraction F2 to a desorption D2 which consists of separating said fraction F2 into a fraction enriched with ethylene (fraction B) and into a fraction F3, optionally containing the 1,2-dichloroethane formed in the chlorination reactor R2 then extracted, if it has not previously been extracted, which is recycled to the absorption A, optionally after an additional treatment intended to reduce the concentration, in said fraction F3, of the compounds that are heavier than ethane; g) conveying said fraction B to an oxychlorination reactor in which most of the ethylene present in said fraction B is converted into 1,2-dichloroethane, wherein the 1,2-dichloroethane so obtained is separated from the stream of products derived from the oxychlorination reactor and is optionally added to the 1,2-dichloroethane formed in the chlorination reactor R1 and optionally to that formed in the chlorination reactor R2; and h) optionally, recycling to step a) the stream of products derived from the oxychlorination reactor, from which the 1,2-dichloroethane has been extracted, optionally containing an additional stream of ethane previously introduced in one of steps b) to g), after having been optionally purged of gases and/or after an optional treatment in order to eliminate the chlorinated products contained therein.
 2. The process according to claim 1, wherein the source of ethane contains at least 80 vol % of ethane.
 3. The process according to claim 1, wherein the source of ethane contains at least 98 vol % of ethane.
 4. The process according to claim 1, wherein the catalytic oxydehydrogenation from step a) takes place at a temperature less than or equal to 650° C.
 5. The process according to claim 1, wherein during step b), said gas mixture is washed then dried, thus producing a dry gas mixture.
 6. The process according to claim 1, wherein during step c) of absorption A, the dry gas mixture is brought into contact with a washing agent containing 1,2-dichloroethane.
 7. The process according to claim 1, wherein said fraction A contains at least 70 wt % of the compounds that are lighter than ethylene contained in the dry gas mixture.
 8. The process according to claim 1, wherein said fraction F1 contains at most 30 wt % of the compounds that are lighter than ethylene contained in the dry gas mixture.
 9. The process according to claim 8, wherein said fraction C contains at least 80 wt % of the compounds that are lighter than ethylene contained in said fraction F1.
 10. A process for manufacturing vinyl chloride, comprising: a) subjecting the stream of ethane to a catalytic oxydehydrogenation thus producing a gas mixture containing ethylene, unconverted ethane, water and secondary constituents; b) drying said gas mixture thus producing a dry gas mixture, wherein said gas mixture is optionally washed before or after said drying; c) after an optional additional purification step, subjecting said dry gas mixture comprising the stream of products derived from the chlorination reactor R2 separated in step e) to an absorption A which consists of separating said gas mixture into a fraction enriched with the compounds that are lighter than ethylene containing some of the ethylene (fraction A) and into a fraction F1; d) conveying said fraction A to a chlorination reactor R1 in which most of the ethylene present in said fraction A is converted into 1,2-dichloroethane, wherein the 1,2-dichloroethane so obtained is separated from the stream of products derived from the chlorination reactor R1; e) subjecting said fraction F1 to a desorption D1 which consists of separating said fraction F1 into an ethylene fraction depleted of the compounds that are lighter than ethylene (fraction C) which is conveyed to a chlorination reactor R2, the stream of products derived from this reactor being added to the dry gas mixture subjected to step c) after having optionally extracted the 1,2-dichloroethane formed, and into a fraction F2; f) subjecting said fraction F2 to a desorption D2 which consists of separating said fraction F2 into a fraction enriched with ethylene (fraction B) and into a fraction F3, optionally containing the 1,2-dichloroethane formed in the chlorination reactor R2 then extracted, if it has not previously been extracted, which is recycled to the absorption A, optionally after an additional treatment intended to reduce the concentration, in said fraction F3, of the compounds that are heavier than ethane; g) conveying said fraction B to an oxychlorination reactor in which most of the ethylene present in said fraction B is converted into 1,2-dichloroethane, wherein the 1,2-dichloroethane so obtained is separated from the stream of products derived from the oxychlorination reactor and is optionally added to the 1,2-dichloroethane formed in the chlorination reactor R1 and optionally to that formed in the chlorination reactor R2; h) optionally, recycling to step a) the stream of products derived from the oxychlorination reactor, from which the 1,2-dichloroethane has been extracted, optionally containing an additional stream of ethane previously introduced in one of steps b) to g), after having been optionally purged of gases and/or after an optional treatment in order to eliminate the chlorinated products contained therein; and i) subjecting the 1,2-dichloroethane so obtained to a pyrolysis thus producing vinyl chloride.
 11. A process for the manufacture of polyvinyl chloride, comprising: a) subjecting the stream of ethane to a catalytic oxydehydrogenation thus producing a gas mixture containing ethylene, unconverted ethane, water and secondary constituents; b) drying said gas mixture thus producing a dry gas mixture, wherein said gas mixture is optionally washed before or after said drying; c) after an optional additional purification step, subjecting said dry gas mixture comprising the stream of products derived from the chlorination reactor R2 separated in step e) to an absorption A which consists of separating said gas mixture into a fraction enriched with the compounds that are lighter than ethylene containing some of the ethylene (fraction A) and into a fraction F1; d) conveying said fraction A to a chlorination reactor R1 in which most of the ethylene present in said fraction A is converted 1,2-dichloroethane, wherein the 1,2-dichloroethane so obtained is separated from the stream of products derived from the chlorination reactor R1; e) subjecting said fraction F1 to a desorption D1 which consists of separating said fraction F1 into an ethylene fraction depleted of the compounds that are lighter than ethylene (fraction C) which is conveyed to a chlorination reactor R2, the stream of products derived from this reactor being added to the dry gas mixture subjected to step c) after having optionally extracted the 1,2-dichloroethane formed, and into a fraction F2; f) subjecting said fraction F2 to a desorption D2 which consists of separating said fraction F2 into a fraction enriched with ethylene (fraction B) and into a fraction F3, optionally containing the 1,2-dichloroethane formed in the chlorination reactor R2 then extracted, if it has not previously been extracted, which is recycled to the absorption A, optionally after an additional treatment intended to reduce the concentration, in said fraction F3, of the compounds that are heavier than ethane; g) conveying said fraction B to an oxychlorination reactor in which most of the ethylene present in said fraction B is converted into 1,2-dichloroethane, wherein the 1,2-dichloroethane so obtained is separated from the stream of products derived from the oxychlorination reactor and is optionally added to the 1,2-dichloroethane formed in the chlorination reactor R1 and optionally to that formed in the chlorination reactor R2; and h) optionally, recycling to step a) the stream of products derived from the oxychlorination reactor, from which the 1,2-dichloroethane has been extracted, optionally containing an additional stream of ethane previously introduced in one of steps b) to g), after having been optionally purged of gases and/or after an optional treatment in order to eliminate the chlorinated products contained therein; i) subjecting the 1,2-dichloroethane so obtained to a pyrolysis thus producing vinyl chloride; and j) polymerizing the vinyl chloride to produce polyvinyl chloride.
 12. The process according to claim 1, wherein mixed oxides containing both Mo and V; W and V or Mo; or W and V are used as a catalytic system to carry out the catalytic oxydehydrogenation.
 13. The process according to claim 12, wherein the mixed oxides are selected from the group consisting of Mo—W—V—Ta—Te—Ti—P—Ni—Ce—O, Mo—W—V—Ta—Te—Ti—P—O, Mo—W—V—Te—Ti—P—Ce—O, Mo—W—V—Te—Ti—P—Ni—O, Mo—W—V—Te—Ti—P—O, Mo—W—V—Te—Ti—O, Mo—W—V—Te—P—O, Mo—W—V—Te—O, Mo—W—V—Ta—Te—Ti—P—Ni—Ce—O, Mo—W—V—Ta—Te—Ti—P—O, Mo—W—V—Te—Ti—P—Ce—O, Mo—W—V—Te—Ti—P—Ni—O, Mo—W—V—Te—Ti—P—O, Mo—W—V—Te—Ti—O, Mo—W—V—Te—P—O, Mo—W—V—Te—O, Mo—W—V—Nb—O, Mo—W—V—Sb—O, Mo—W—V—Ti—Sb—Bi—O, Mo—W—V—Ti—Sb—O, Mo—W—V—Sb—Bi—O, Mo—W—V—Zr—O, Mo—W—V—Nb—Ta—O, Mo—W—V—Nb—O, and Mo—W—V—O.
 14. The process according to claim 10, wherein said fraction A contains at least 70 wt % of the compounds that are lighter than ethylene contained in the dry gas mixture.
 15. The process according to claim 10, wherein said fraction C contains at least 80 wt % of the compounds that are lighter than ethylene contained in said fraction F1.
 16. The process according to claim 10, wherein mixed oxides containing both Mo and V; W and V or Mo; or W and V are used as a catalytic system to carry out the catalytic oxydehydrogenation.
 17. The process according to claim 16, wherein the mixed oxides are selected from the group consisting of Mo—W—V—Ta—Te—Ti—P—Ni—Ce—O, Mo—W—V—Ta—Te—Ti—P—O, Mo—W—V—Te—Ti—P—Ce—O, Mo—W—V—Te—Ti—P—Ni—O, Mo—W—V—Te—Ti—P—O, Mo—W—V—Te—Ti—O, Mo—W—V—Te—P—O, Mo—W—V—Te—O, Mo—W—V—Ta—Te—Ti—P—Ni—Ce—O, Mo—W—V—Ta—Te—Ti—P—O, Mo—W—V—Te—Ti—P—Ce—O, Mo—W—V—Te—Ti—P—Ni—O, Mo—W—V—Te—Ti—P—O, Mo—W—V—Te—Ti—O, Mo—W—V—Te—P—O, Mo—W—V—Te—O, Mo—W—V—Nb—O, Mo—W—V—Sb—O, Mo—W—V—Ti—Sb—Bi—O, Mo—W—V—Ti—Sb—O, Mo—W—V—Sb—Bi—O, Mo—W—V—Zr—O, Mo—W—V—Nb—Ta—O, Mo—W—V—Nb—O, and Mo—W—V—O.
 18. The process according to claim 11, wherein said fraction A contains at least 70 wt % of the compounds that are lighter than ethylene contained in the dry gas mixture.
 19. The process according to claim 11, wherein said fraction C contains at least 80 wt % of the compounds that are lighter than ethylene contained in said fraction F1.
 20. The process according to claim 11, wherein mixed oxides containing both Mo and V; W and V or Mo; or W and V are used as a catalytic system to carry out the catalytic oxydehydrogenation.
 21. The process according to claim 20, wherein the mixed oxides are selected from the group consisting of Mo—W—V—Ta—Te—Ti—P—Ni—Ce—O, Mo—W—V—Ta—Te—Ti—P—O, Mo—W—V—Te—Ti—P—Ce—O, Mo—W—V—Te—Ti—P—Ni—O, Mo—W—V—Te—Ti—P—O, Mo—W—V—Te—Ti—O, Mo—W—V—Te—P—O, Mo—W—V—Te—O, Mo—W—V—Ta—Te—Ti—P—Ni—Ce—O, Mo—W—V—Ta—Te—Ti—P—O, Mo—W—V—Te—Ti—P—Ce—O, Mo—W—V—Te—Ti—P—Ni—O, Mo—W—V—Te—Ti—P—O, Mo—W—V—Te—Ti—O, Mo—W—V—Te—P—O, Mo—W—V—Te—O, Mo—W—V—Nb—O, Mo—W—V—Sb—O, Mo—W—V—Ti—Sb—Bi—O, Mo—W—V—Ti—Sb—O, Mo—W—V—Sb—Bi—O, Mo—W—V—Zr—O, Mo—W—V—Nb—Ta—O, Mo—W—V—Nb—O, and Mo—W—V—O. 